Nebulin is an actin-binding protein which is localized to the thin filament of the sarcomeres in skeletal muscle. Nebulin in humans is coded for by the gene NEB. It is a very large protein (600–900 kDa) and binds as many as 200 actin monomers. Because its length is proportional to thin filament length, it is believed that nebulin acts as a thin filament "ruler" and regulates thin filament length during sarcomere assembly. Other functions of nebulin, such as a role in cell signaling, remain uncertain.
Nebulin has also been shown to regulate actin-myosin interactions by inhibiting ATPase activity in a calcium-calmodulin sensitive manner.
Mutations in nebulin cause some cases of the autosomal recessive disorder nemaline myopathy.
A smaller member of the nebulin protein family, termed nebulette, is expressed in cardiac muscle.
